The present disclosure relates to a blowout preventer. In particular, although not exclusively, the present disclosure relates to a blowout preventer for an oil or gas well.
Blowout preventers (BOPs) for oil or gas wells are used to prevent potentially catastrophic events known as a blowouts, where high pressures and uncontrolled flow from a well reservoir can blow tubing (e.g. drill pipe and well casing), tools and drilling fluid out of a wellbore. Blowouts present a serious safety hazard to drilling crew, the drilling rig and the environment and can be extremely costly.
Typically BOPs have rams that are hydraulically pushed across the wellbore to close off the wellbore. In some cases the rams have hardened steel shears to cut through a drill string which may be in the wellbore.
A problem with many of the hydraulically actuated rams is that they require a large amount of hydraulic force to move the rams against the pressure inside the wellbore and to cut through drill strings.
An additional problem with hydraulically actuated rams is that the hydraulic force is typically generated away from the blowout preventer, making the blowout preventer susceptible to failure if the hydraulic line conveying the hydraulic force is damaged. Further problems may include the erosion of cutting and sealing surfaces due to the relatively slow closing action of the rams in a flowing wellbore. Cutting through tool joints, drill collars, large diameter tubulars and off centre drill strings under heavy compression may also present problems for hydraulically actuated rams.
Typically, once the rams have closed off the wellbore and the well has been brought under control, the rams are either retracted or drilled through so that drilling may be resumed.
It will be clearly understood that any reference herein to background material or information, or to a prior publication, does not constitute an admission that any material, information or publication forms part of the common general knowledge in the art, or is otherwise admissible prior art.